Do predation and host plant quality interact to regulatesoybean aphid?

Landis, D., A. Costamagna, K. Thelen, C. DiFonzo, M. O'Neal

Presented at the All Scientist Meeting (2004-10-08 )

The soybean aphid (Aphis glycines Matsumura) is an invasive species from Asia that has become a major pest of soybean in the US since its discovery in 2000. Prior research has shown that existing natural enemy communities contribute to A. glycines population regulation in Michigan soybeans and can result in effective economic control. The differential disturbance gradients represented on the KBS LTER site are likely to influence A. glycines population regulation via two mechanisms. First, 14 years of differential management on the KBS LTER site have created differences in generalist natural enemy assemblages that may regulate the ability of this invasive herbivore to successfully colonize these habitats via top-down influences. Second, by altering soil and nutrient conditions, treatment regimes may alter host plant phenology and nutritional quality through bottom–up effects that may influence A. glycines intrinsic rate of increase. We found no consistent evidence of bottom-up effects of agronomic treatments on aphid increase under a wide range of chemical input levels.  We did detect strong evidence of top-down control on aphid population with predator exclusion resulting in a 3 to 11 fold increase of aphid population in comparison with the controls. Our study suggests that generalist predator communities appear to be more important than host plant quality in regulation aphid population dynamics under the range of agronomic regimes we studied.  However, bottom-up influences could be important in other crops or years.  Our findings also suggest that predation maintained A. glycines populations below estimated economic thresholds for most of the season, and that enhancing natural enemy impacts during the mid-season may be necessary to improve biological control.

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